Affect in mathematics education: an introduction

The article presents an introduction to the concept of affect in mathematics education research

Mobile metal adatoms on single layer, bilayer and trilayer graphene: an ab initio study correlated with experimental electron microscopy data

The plane-wave density functional theory code CASTEP was used with the Tkatchenko-Scheffler van der Waals correction scheme and the generalized gradient approximation of Perdew, Burke, and Ernzerhof (GGA PBE) to calculate the binding energy of Au, Cr, and Al atoms on the armchair and zigzag edge binding sites of monolayer graphene, and at the high-symmetry adsorption sites of single layer, bilayer, and trilayer graphene. All edge site binding energies were found to be substantially higher than the adsorption energies for all metals. The adatom migration activation barriers for the lowest energy migration paths on pristine monolayer, bilayer, and trilayer graphene were then calculated and found to be smaller than or within an order of magnitude of kBT at room temperature, implying very high mobility for all adatoms studied. This suggests that metal atoms evaporated onto graphene samples quickly migrate across the lattice and bind to the energetically favorable edge sites before being characterized in the microscope. We then prove this notion for Al and Au on graphene with scanning transmission electron microscopy (STEM) images showing that these atoms are observed exclusively at edge sites, and also hydrocarbon-contaminated regions, where the pristine regions of the lattice are completely devoid of adatoms. Additionally, we review the issue of fixing selected atomic positions during geometry optimization calculations for graphene/adatom systems and suggest a guiding principle for future studies

Discrete Chiral Symmetry and Mass Shift in Lattice Hamiltonian Approach to Schwinger Model

We revisit the lattice formulation of the Schwinger model using the Kogut-Susskind Hamiltonian approach with staggered fermions. This model, introduced by Banks et al., contains the mass term $m_{\rm lat} \sum_{n} (-1)^{n} \chi^\dagger_n \chi_n$, and setting it to zero is often assumed to provide the lattice regularization of the massless Schwinger model. We instead argue that the relation between the lattice and continuum mass parameters should be taken as $m_{\rm lat}=m- \frac 18 e^2 a$. The model with $m=0$ is shown to possess a discrete chiral symmetry that is generated by the unit lattice translation accompanied by the shift of the $\theta$-angle by $\pi$. While the mass shift vanishes as the lattice spacing $a$ approaches zero, we find that including this shift greatly improves the rate of convergence to the continuum limit. We demonstrate the faster convergence using both numerical diagonalizations of finite lattice systems, as well as extrapolations of the lattice strong coupling expansions.Comment: 14 pages, 7 figures; v2 refs added, minor improvement

Atomically resolved structural determination of graphene and its point defects via extrapolation assisted phase retrieval

Previously reported crystalline structures obtained by an iterative phase retrieval reconstruction of their diffraction patterns seem to be free from displaying any irregularities or defects in the lattice, which appears to be unrealistic. We demonstrate here that the structure of a nanocrystal including its atomic defects can unambiguously be recovered from its diffraction pattern alone by applying a direct phase retrieval procedure not relying on prior information of the object shape. Individual point defects in the atomic lattice are clearly apparent. Conventional phase retrieval routines assume isotropic scattering. We show that when dealing with electrons, the quantitatively correct transmission function of the sample cannot be retrieved due to anisotropic, strong forward scattering specific to electrons. We summarize the conditions for this phase retrieval method and show that the diffraction pattern can be extrapolated beyond the original record to even reveal formerly not visible Bragg peaks. Such extrapolated wave field pattern leads to enhanced spatial resolution in the reconstruction.Comment: 10 pages, 4 figure

Phase Diagram of the Two-Flavor Schwinger Model at Zero Temperature

We examine the phase structure of the two-flavor Schwinger model as a function of the $\theta$-angle and the two masses, $m_1$ and $m_2$. In particular, we find interesting effects at $\theta=\pi$: along the $SU(2)$-invariant line $m_1 = m_2 = m$, in the regime where $m$ is much smaller than the charge $g$, the theory undergoes logarithmic RG flow of the Berezinskii-Kosterlitz-Thouless type. As a result, in this regime there is a non-perturbatively small mass gap $\sim e^{- A g^2/m^2}$. The $SU(2)$-invariant line lies within a region of the phase diagram where the charge conjugation symmetry is spontaneously broken and whose boundaries we determine numerically. Our numerical results are obtained using the Hamiltonian lattice gauge formulation that includes the mass shift $m_\text{lat} = m- g^2 a/4$ dictated by the discrete chiral symmetry.Comment: 7 pages, 3 figures; v2 minor improvements, refs adde

Enhancing the evaporative cooling performance of fan-pad system using alternative pad materials and water film over the greenhouse roof

Greenhouse technology is a viable option for sustainable crop production in the regions of adverse climatic conditions.  During hot seasons the heat input to a greenhouse causes the internal temperature to exceed its optimal value.  The present study was devoted to construct an evaporative cooling system to reduce heat stress inside a greenhouse.  Two identical small-scale greenhouses were designed, constructed, and installed on an open roof of a domestic house.  The two greenhouses were cooled using fan-pad system.  In addition, a thin water film was applied on the roof of one greenhouse to study the effect of roof water film and fan-pad (combined system) on the cooling performance.  The two cooling systems were compared under the same condition.  Three new evaporative cooling pads represented by Cryperus Alopecuroides Rottb (Samar), Cyerus Alternifolius (Purdy) and Cyperus Rotundus l (Nut-grass or Se'd) were adapted and evaluated.  Three pad face air velocities ranged between 0.45 and 1.01 m s-1 and two thicknesses of 10 and 15 cm were used in the investigation of the cooling performance criteria.  Results showed that the proposed cooling pads in the suggested evaporative cooling systems were able to maintain acceptable microclimatic conditions for greenhouse models.  Se'd pad material proved more efficiency in temperature reduction.  It was revealed that the temperature inside the greenhouse operated under the combination of roof water flow and fan-pad system was less than that for fan-pad greenhouse by about 1.1 to 5.44° C in the morning and afternoon respectively.  The air relative humidity was increased due to humid effect provided by cooling system which protects crops from excessive transpiration and crop damage.  The daily average cooling efficiencies of 88.4, 83.1 and 79.6% were obtained for Se'd, Purdy and Samar, respectively during testing days inside the combined system at 15 cm pad thickness and 0.45 m s-1 pad face air velocity.  The Se'd pad material showed the highest efficiency as compared to other pad materials and could be used as an alternative pad material.   Keywords: greenhouse, evaporative cooling, fan-pad system, pad material, roof water flo

Gait recognition using kinect and locally linear embedding

This paper presents the use of locally linear embedding (LLE) as feature extraction technique for classifying a person’s identity based on their walking gait patterns. Skeleton data acquired from Microsoft Kinect camera were used as an input for (1). Multilayer Perceptron (MLP) and (2). LLE with MLP. The MLP classification accuracy result was used for comparison between both. Several MLP and LLE properties were tested to find the optimal number of setting that can improve the MLP performance. Based on the two methods used, the neural network implemented with LLE showed the better accuracy compared to the neural network alone.Keywords: locally linear embedding; neural network; multilayer perceptron

Sustainable Cost Models for mHealth at Scale: Modeling Program Data from m4RH Tanzania

BackgroundThere is increasing evidence that mobile phone health interventions (“mHealth”) can improve health behaviors and outcomes and are critically important in low-resource, low-access settings. However, the majority of mHealth programs in developing countries fail to reach scale. One reason may be the challenge of developing financially sustainable programs. The goal of this paper is to explore strategies for mHealth program sustainability and develop cost-recovery models for program implementers using 2014 operational program data from Mobile for Reproductive Health (m4RH), a national text-message (SMS) based health communication service in Tanzania.MethodsWe delineated 2014 m4RH program costs and considered three strategies for cost-recovery for the m4RH program: user pay-for-service, SMS cost reduction, and strategic partnerships. These inputs were used to develop four different cost-recovery scenarios. The four scenarios leveraged strategic partnerships to reduce per-SMS program costs and create per-SMS program revenue and varied the structure for user financial contribution. Finally, we conducted break-even and uncertainty analyses to evaluate the costs and revenues of these models at the 2014 user volume (125,320) and at any possible break-even volume.ResultsIn three of four scenarios, costs exceeded revenue by $94,596,$34,443, and $84,571 at the 2014 user volume. However, these costs represented large reductions (54$203,475. Scenario four, in which the lowest per-SMS rate ($0.01 per SMS) was negotiated and users paid for all m4RH SMS sent or received, achieved a$5,660 profit at the 2014 user volume. A Monte Carlo uncertainty analysis demonstrated that break-even points were driven by user volume rather than variations in program costs.ConclusionsThese results reveal that breaking even was only probable when all SMS costs were transferred to users and the lowest per-SMS cost was negotiated with telecom partners. While this strategy was sustainable for the implementer, a central concern is that health information may not reach those who are too poor to pay, limiting the program’s reach and impact. Incorporating strategies presented here may make mHealth programs more appealing to funders and investors but need further consideration to balance sustainability, scale, and impact

Ісак Мазепа: перші кроки у великій політиці

Досліджується становлення світоглядних позицій та формування політичних поглядів І. Мазепи.Исследуется становление мировоззренческих позиций и формирование политических взглядов И. Мазепы.Formation world outlook positions and formation of political views of I. Mazepa is investigated